Short of hooking the gauges up to a car and testing them I think you really need to just get a gauge place to do it.

The loom is as 1Badvan said, just repair as needed.

One tip, in the wb service manual it says..... do NOT operate or test the temp/fuel gauges without the earth hooked up! Instantly rooted!

Try and buy a genuine GMH service manual. I have the HJ and WB updates and they have terrific wiring diagrams and heaps of other technical stuff in them.